Gotta be two different things. Basically ad4 had a DMA error and
detached and the HAMMER filesystem, being unable to write, threw a fit.
That would be an issue with NATA. HAMMER was just saving itself.

That sort of UDMA failure is usually indicative of an IDE wiring
issue.

We did fix a bug in HAMMER related to very rare incorrect B-Tree
deletions which would lead to lost inodes and potentially panics.
Anything like that should no longer occur.

Wiring was the one possibility, and underpowered drive could be just
another (P4/2.4 with 3 HDD's on noname 300W PSU). Just realized that
few days ago: mbmon's 12P had showed 10.5+ Volts until PSU was
replaced with 400W one.